1. Field of the Invention
The present invention relates to hybrid copolymers of synthetic and naturally derived materials. More particularly, the present invention is directed towards chain transfer agents formed from hydroxyl-containing naturally derived materials for use during production of synthetic polymers to produce those hybrid copolymers. The present invention also relates to anti-scalant and/or dispersant formulations or compositions including such polymers and their use in aqueous systems, including scale minimization.
2. Background Information
Many aqueous industrial systems require various materials to remain in a soluble, suspended or dispersed state. Examples of such aqueous systems include boiler water or steam generating systems, cooling water systems, gas scrubbing systems, pulp and paper mill systems, desalination systems, fabric, dishware and hard surface cleaning systems, as well as downhole systems encountered during the production of gas, oil, and geothermal wells. Often the water in those systems either naturally or by contamination contains ingredients such as inorganic salts. These salts can cause accumulation, deposition, and fouling problems in aqueous systems such as those mentioned above.
Inorganic salts are typically formed by the reaction of metal cations (e.g., calcium, magnesium or barium) with inorganic anions (e.g., phosphate, carbonate or sulfate). When formed, the salts tend to be insoluble or have low solubility in water. As their concentration in solution increases or as the pH and/or temperature of the solution containing those salts changes, the salts can precipitate from solution, crystallize and form hard deposits or scale on surfaces. Such scale formation is a problem in equipment such as heat transfer devices, boilers, secondary oil recovery wells, and automatic dishwashers, as well as on substrates washed with such hard waters, reducing the performance and life of such equipment.
In addition to scale formation many cooling water systems made from carbon steel, including industrial cooling towers and heat exchangers, experience corrosion problems. Attempts to prevent this corrosion are often made by adding various inhibitors such as orthophosphate and/or zinc compounds to the water. However, phosphate addition increases the formation of highly insoluble phosphate salts such as calcium phosphate. The addition of zinc compounds can lead to precipitation of insoluble salts such as zinc hydroxide and zinc phosphate.
Other inorganic particulates such as mud, silt and clay can also be commonly found in cooling water systems. These particulates tend to settle onto surfaces, thereby restricting water flow and heat transfer unless they are effectively dispersed.
Stabilization of aqueous systems containing scale-forming salts and inorganic particulates involves a variety of mechanisms. Inhibition is one conventional mechanism for eliminating the deleterious effect of scale-forming salts. In inhibition, synthetic polymer(s) are added that increase the solubility of the scale-forming salt in the aqueous system.
Another stabilization mechanism is the dispersion of precipitated salt crystals. Synthetic polymers having carboxylic acid groups function as good dispersants for precipitated salts such as calcium carbonates. In this mechanism, the crystals stay dispersed rather than dissolving in the aqueous solution.
A third stabilization mechanism involves interference and distortion of the crystal structure of the scale by the polymer, thereby making the scale less adherent to surfaces, other forming crystals and/or existing particulates.
Synthetic polymers can also impart many useful functions in cleaning compositions. For example, they can function either independently or concurrently as viscosity reducers in processing powdered detergents. They can also serve as anti-redeposition agents, dispersants, scale and deposit inhibitors, crystal modifiers, and/or detergent assistants capable of partially or completely replacing materials used as builders while imparting optimum detergent action properties to surfactants.
Cleaning formulations contain builders such as phosphates and carbonates for boosting their cleaning performance. These builders can precipitate out insoluble salts such as calcium carbonate and calcium phosphate in the form of calcium orthophosphate. The precipitants form deposits on clothes and dishware that results in unsightly films and spots on these articles. Similarly, insoluble salts cause major problem in down hole oil field applications. Hence, there is a need for polymers that will minimize the scaling of insoluble salts in water treatment, oil field and cleaning formulations.
Synthetic polymers have been used to minimize scale formation in aqueous treatment systems for a number of years. However, there has been a shortage of monomers to produce these synthetic polymers lately due to rising demand and tight crude oil supplies. Hence, there is a need to replace these synthetic polymers with hybrid polymers that are at least partially derived from renewal natural sources. Also, polymers from renewal natural sources should have a better biodegradable profile than synthetic polymers, which tend to have very little biodegradability.
A number of attempts have been made in the past to use natural materials as polymeric building blocks. These have mainly centered on grafting natural materials like sugars and starches with synthetic monomers. For example, U.S. Pat. Nos. 5,854,191, 5,223,171, 5,227,446 and 5,296,470 disclose the use of graft copolymers in cleaning applications.
Graft copolymers are produced by selectively generating initiation sites (e.g., free radicals) for the growth of monomer side chains from the saccharide or polysaccharide backbone (CONCISE ENCYCLOPEDIA OF POLYMER SCIENCE AND ENGINEERING, J. I. Kroschwitz, ed., Wiley-Interscience, New York, p. 436 (1990)). These grafting techniques typically use Fe(II) salts such as ferrous sulfate or Ce(IV) salts (e.g., cerium nitrate or cerium sulfate) to create those initiation sites on the saccharide or polysaccharide backbone (see, e.g., U.S. Pat. No. 5,304,620). Such redox processes are not easily controlled, are inefficient and generate unwanted homopolymers. Also, cerium salts tend to be left in the resulting solution as unwanted byproducts, thereby presenting a potential negative effect on performance. Therefore, there is a need for natural materials as polymeric building blocks that do not provide those problems associated with graft copolymers.